Three-dimensional apertured formed film topsheets, or the acquisition distribution layer interposed between the topsheet and the core of absorptive devices, having both three-dimensional micro-apertures facing upward toward the skin side of users of absorptive devices and three-dimensional macro-apertures interspersed in a pattern within the field of three-dimensional micro-apertures, the macro-apertures facing downward toward the absorbent core, are well known in the art. The three-dimensional micro-apertures are known to provide a tactile impression of cottony soft, cloth-like or silky textures while also enhancing the reduction of the amount of surface wetness after use.
Such films may be produced using one of several methods, including vacuum-forming process and hydro-forming process. In both these methods, the film is deposited on a rotating screen having openings corresponding to a desired micro-aperture pattern. In vacuum-forming, a relative vacuum is established across the screen so that the film is drawn into the openings, thereby forming a series of protrusions on the film surface. If the vacuum differential is sufficient, an opening is formed in the film at the apex of each protrusion. In hydro-forming, similar protrusions are formed by directing a high pressure water stream at the side of the film opposite of the screen. The pressure of the water stream forces the film into the holes of the screen. If sufficient pressure is applied, an opening is formed in the film at the apex of each protrusion.
Micro-apertures can also be formed using mechanical methods such as needle punching, but such methods tend to require additional steps to provide the three dimensionality that tends to enhance the perceived softness of the final material.
In U.S. Pat. No. 4,609,518 to Curro et al. (“Curro '518”), a polymeric web can be produced using one or more three-dimensional forming structures, essentially a parent patent to the “hydro-forming process”, it is taught that three-dimensional micro-aperture patterns of high mesh count are formed by a high pressure water stream “. . . having filaments [or lands]. . . ranging in diameter [or land width] from about 3 mils to about 7 mils and mesh counts ranging from about 140 by 140 per square inch to about 80 by 80 per square inch, respectively, will typically produce very soft feeling three-dimensional apertured webs when subjected to the high pressure liquid jet[s]. . . issuing from nozzle[s]. . . . The relatively small three-dimensional apertures created in such webs substantially correspond to the void spaces [or openings] created in the interstices . . . between the intersecting filaments [or lands].” The three-dimensional macro-apertures are then formed in a second stage process where that forming screen has large openings of a lower mesh count as designed to be suitable for adequate fluid acquisition through the topsheet into the absorbent core of absorptive device.
Premium ALWAYS° brand feminine hygiene pads, sold by Procter & Gamble Co., Ohio, utilize a topsheet substantially produced by the hydroforming process of Curro '518. The three-dimensional micro-aperture pattern, when counted from a purchased pad from any of a variety of Retail Stores, is generally around 100 mesh. It is known for its cottony soft tactile impression which renders both comfort and cleanliness to the user. When viewing the three-dimensional micro-apertures under magnification, they have an elongation, or major axis, in the machine direction (MD). The MD corresponds to the length or front-to-back direction of the feminine pad. Many are somewhat pointed at the extreme ends of their major axes. They appear in shape to be very similar to the iris of a ‘cat-eye’, thus here-in-after their shape will be known as a ‘cat-eye’ shape. This cat-eye shape is common for three-dimensional apertures formed in the hydroforming process of the prior art.
Three-dimensional macro-apertures can be formed into a ‘precursor’ web already comprising a pattern of softening three-dimensional micro-apertures. A second stage of hydroforming is used in Curro '518. Other methods use a roller with a pattern of needles, pins or similar protrusions with the protrusions being pushed through the precursor web into a malleable, easily penetrated material, or, ideally, into a corresponding pattern of depression such as grooves, slots or cavities. Typically the protruding direction of the micro-apertures is up and the protruding direction of the macro-apertures is down.
U.S. Pat. No. 8,168,102 to Di Berardino (“Di Berardino '102”) discloses one mechanical punching method. In its abstract, it describes: “A machine utilized for producing and manufacturing a film, soft at touch, resilient and suitable at draining use. A film produced by such a machine, presents, at least, on one surface an essentially continuous pattern of micro-funnels three-dimensional (3D) directed in an essentially perpendicular way to the surface from which the micro-openings have origin. It presents also on the opposite surface a continuous pattern, composed by 3D macro-funnels directed in an essentially perpendicular way to the surface from which the macro-funnels have origin. The “micro-funnels” term, intend to describe a multitude of funnels non-distinguishable by the human eye at a distance equal or higher than 450 mm, while the “macro-funnels” term, intend to describe funnels clearly visible by the human eye at a distance higher than 450 mm.”
Claim 9 of Di Berardino '102 further describes the method: “A device for forming a thermoplastic film with macro holes from a film already having micro holes, comprising: a first reel with multiple needles on its surface; a second reel with multiple grooves, the grooves coupled to the needles during the rotation of the first and second reels to obtain the macro holes; and a third reel with perforations, the perforations being coupled with the needles of the first reel during rotation of the first reel to remove the thermoplastic film from the first reel without substantially damaging the micro holes, wherein the third reel uses electrostatic electricity to remove the thermoplastic film from the first reel by exerting a force via the electrostatic electricity on the macro holes of the thermoplastic film.”
U BY KOTEX® brand feminine napkins, sold by Kimberly-Clark Corporation, utilize this type of topsheet material and call it an Xpress DRI® cover. The three-dimensional micro-aperture pattern, when counted from a purchased pad from any of a variety of Retail Stores, is generally around 60 mesh. It is also known for its cottony soft tactile impression which renders both comfort and cleanliness to the user. When viewing the three-dimensional micro-apertures under magnification they are essentially round, as is common for three-dimensional apertures formed in a vacuum forming process.
Additionally, it is known that sufficient open area of the three-dimensional micro-apertured web, as with any three-dimensional apertured web, is required not only for adequate softness, but also to assist with fluid acquisition related to surface cleanliness after use. While the 100 mesh hydroformed pattern is proven to be sufficiently soft and clean, 100 mesh to about 75 mesh patterns will not form good three-dimensional aperture openings by the vacuum forming method due to its limited maximum pressure differential of slightly less than one negative atmosphere—about 14.0 PSI. Smaller openings require higher force to create an opening like the multiple hundreds PSI of hydro-forming. Therefore, the film's open area achievable by vacuum forming, virtually approaching zero percent as mesh counts increase beyond 75 mesh, is insufficient for good performance in reducing residual surface wetness after use. The smaller opening sizes and lack of thinning at the apex can also negatively affect the perception of softness.
Conversely, the lower mesh count versions in the range of micro-apertures from about 40 to about 75 mesh, that form good round openings with sufficient open area in the vacuum forming process, will not form openings with sufficient open area for fluid acquisition dynamics or sufficient softness properties when produced by the hydroforming process. Logically, the cat-eye shape of hydroforming, increasingly more dramatic within these micro-aperture mesh counts, where the forming screens have progressively larger openings, reduces the resulting film's open area. While a circle's major axis (i.e., its diameter) exists in all directions, the cat-eye shape (which may be an ellipse or other ovate figure) has a major axis value in one direction and a minor axis value in the other direction. Thus, the cat-eye shape has a lower opening area than a circle having the same major axis value. Hydro-forming also creates a smaller aperture in general, so its major axis will be less than the value of the circle's axis, which compounds the loss of open area.
This difference occurs primarily because, in vacuum forming methods, the polymer web is provided in molten form, and is therefore completely pliable and formable. As a result, the pressure differential due to the vacuum causes the molten material to mold itself against the walls of the aperture. In that last moment of being molten, it essentially forms an exact replicate of the screen aperture. As it cools to a solid state, however, it shrinks. This shrinkage reduces the film aperture dimensions to only a percentage of the screen aperture dimensions.
Conversely, hydro-forming processes involve placing a solid (i.e., non-molten) film web over the forming screen. Such a web requires a higher pressure differential to distort and re-shape the solid film into its new three dimensional aperture form. The film is not molded, as is the molten web of vacuum forming, but rather is stretched and distorted or deformed by pressure; hence, the cat-eye shape results as seen in the higher mesh counts needed for softness.
The hydro-forming film's resulting cat-eye is also the cause of the poor softness properties.